Kerry: 'The case is going to build stronger and stronger'

9/1/13 9:22 AM EDT

Secretary of State John Kerry on Sunday said the “rationale for the military response" being sought by President Barack Obama "will be as powerful if not more powerful each day.

Appearing on “Fox News Sunday, Kerry added, “The fact is that, yesterday, we have now learned that hair and blood samples that have come to us from east Damascus, from individuals who were engaged as first responders in east Damascus, I can report to you today they have tested positive for signatures of sarin. “

“So, this case is going to build stronger and stronger, and the president believes that the United States of America for a decision like this is stronger when you have the time to be able to have the support of the United States Congress and obviously the support of the American people through them,” he added.

Kerry said he believes “people should be celebrating that the president is not moving unilaterally.”

“That he is honoring the request that he heard from many people in Congress, to consult and to be engaged with them, and I think realizing that the Assad regime is already on the defensive,” he said. “They are being significantly impacted by the potential of these strikes. We do not lose anything. We actually gain, and what we gain is the legitimacy of the full-throated response of the Congress of the United States and the president, acting together after our democratic process has worked properly.”

The United States’ “credibility is on the line here,” Kerry said, but added that in the end he believes Congress will approve the action.